Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $180.52   12.259%   $202.6499   $202.65   $202.65   $202.60  
  Purchase #2 $244.73   7.705%   $263.5864   $263.59   $263.60   $263.60  
  Purchase #3 $29.66   13.695%   $33.7219   $33.72   $33.70   $33.70  
  Purchase #4 $150.33   5.493%   $158.5876   $158.59   $158.60   $158.60  
  Purchase #5 $111.96   8.334%   $121.2907   $121.29   $121.30   $121.30  
  Purchase #6 $40.34   9.330%   $44.1037   $44.10   $44.10   $44.10  
  Purchase #7 $176.46   12.617%   $198.724   $198.72   $198.70   $198.70  
  7 purchase totals = $934.00       $1,022.6642   $1,022.66   $1,022.65   $1,022.60